The present invention relates to a poly-p-phenylene sulfide resin composition and a film made thereof. More particularly, it relates to a chemically stabilized poly-p-phenylene sulfide resin composition and a film made thereof.
Poly-p-phenylene sulfide is a thermoplastic crystalline engineering plastic which is superior in thermal resistance, electrical insulating properties, chemical resistance, and flame retardancy. It is useful as a raw material for injection molding as well as films and fibers. Molded materials, films, and fibers produced therefrom are suitable as heatproof electrical insulating materials because of their long-term thermal resistance (continuous use at 160.degree. to 200.degree. C.).
However, the use of poly-p-phenylene sulfide as an electrical insulating material has been limited due to the following disadvantages.
First, the conventional poly-p-phenylene sulfide insulating material is subject to so-called "copper contact failure" which is a phenomenon that the insulating material considerably decreases in thermal resistance when it is exposed to a high temperature continuously while in direct contact with copper, as in the case where an insulating film is wound directly around a copper wire.
Secondly, the conventional poly-p-phenylene sulfide insulating material decreases considerably in thermal resistance when it is exposed to a high temperature continuously in the presence of oxygen in an enclosed environment, as in the case where the insulating material is used in an enclosed motor. This phenomenon is less severe when it is used in an open motor.
Thirdly, the conventional poly-p-phenylene sulfide resin composition shortens the life of a mold due to gradual corrosion of the part of the mold in contact with the polymer during injection molding even in applications other than electrical insulation.
The above disadvantages are also found in the biaxially oriented poly-p-phenylene sulfide film for electrical insulation as disclosed in U.S. Pat. No. 4,286,018. This patent discloses that the biaxially oriented poly-p-phenylene sulfide film can contain an additive and/or filler, but this disclosure merely suggests the possibility for incorporating an additive and/or filler and the incorporation of an additive and/or filler is not intended to eliminate the above-mentioned disadvantages. This patent mentions nothing about the improvement in resistance to copper contact and thermal resistance in closed systems which is accomplished by the use of specific additives or fillers described hereinafter.
There is disclosed in U.S. Pat. No. 4,140,671 the addition of a metal oxide such as ZnO and MgO to a polyethylene terephthalate resin composition containing polyphenylene sulfide. According to the disclosure, the metal oxide additive is incorporated merely as a nucleating agent for the polyethylene terephthalate mainly constituting the composition and the presence of the polyethylene terephthalate as a main ingredient is a requisite of this invention. What is disclosed in this patent is not associated with the improvement in the disadvantages of poly-p-phenylene sulfide resin compositions described heretofore. This is apparent from the well known fact that a thermoplastic polyethylene terephthalate resin composition as disclosed in this patent is so poor in thermal resistance it is unable to use for a long time under a high temperature condition where copper contact failure becomes a problem.